PCR amplification and sequencing
A total of 108 DNA sequences were obtained after the amplification and sequencing of L. japonicus samples derived from 27 different regions. All samples were successfully amplified and sequenced from total DNA. The resulting sequences were compared with known sequences in the NCBI database, and the comparison results showed that the samples were homologous with 96.8–99.9% of the known sequences of L. japonicus in the NCBI database, indicating that the amplification and sequencing results were reliable. Sequence analysis showed that the length of different DNA marker sequences ranged from 312 to 698 bp and that the length of the concatenation sequence was 2124 bp. Among the sequences, the psbA-trnH sequence was the shortest at 312 bp and the rbcL sequence was the longest at 698 bp. In a previous study, rbcL and ITS could not be fully amplified using the genomic DNA of Nardostachys jatamansi (D.Don) DC (Wen et al. 2020). However, using the same primers and reaction conditions, rbcL and ITS markers were completely (100%) amplified in the genomic DNA of L. japonicus, indicating that the differences in amplification efficiency may be caused by interspecies differences.
Intraspecific Genetic Distances And Data Distribution
ITS, psbA-trnH, rbcL, and rpoB had 15, 7, 13, and 3 variant sites, respectively. The genetic distances of ITS, psbA-trnH, and rpoB were mostly distributed in the range of 0.000000-0.003500 (Fig. 1); these genetic distances were too small to distinguish the origins. Although genetic differences were most pronounced in rbcL, they did not sufficiently cluster in the subsequent analysis. The distribution of genetic distance showed that the concatenation sequence had good genetic divergence. The intraspecific distance of the concatenation sequence was 0.000000-0.007554. The maximum genetic distance between Guangshui, Hubei, and Yiyang, Jiangxi, was 0.007554, whereas the minimum genetic distances were 0.000000 between Dongchangfu, Shandong, and Shenxian, Shandong; Fushun, Sichuan, and Dujiangyan, Sichuan; and Linqing, Shandong, and Guanxian, Shandong.
Nj Phylogenetic Trees
A phylogenetic analysis of 27 samples of L. japonicus derived from 11 different provinces was performed using four DNA markers (Fig. 2). Based on the ρ-distance model, phylogenetic trees were constructed using the NJ method. The results showed that the phylogenetic trees of different DNA marker methods were different. The psbA-trnH and rpoB markers had low clustering ability and could not distinguish most of the origins, whereas ITS and rpoB had better clustering ability but could not sufficiently cluster for Shandong, Guangdong, Henan, and Hebei. Although psbA-trnH (Li et al. 2019; Philippe et al. 2022) and rpoB (Aydin et al. 2022; Mousavi et al. 2022) are widely used to study traditional Chinese medicine and have good clustering abilities, psbA-trnH and rpoB played a minor role in distinguishing among the different origins of L. japonicus; this may be caused by interspecific differences. By contrast, other DNA markers could not be clustered effectively and the order in the branches of the phylogenetic tree was promiscuous. In the present study, the combination sequence could better distinguish L. japonicus species derived from different origins, and the results showed interspecific genetic differences in the same species (Fig. 3). The concatenation sequence clustered L. japonicus of the same origin together, validating the method employed in this study. Therefore, it is important to use a concatenation sequence to cluster L. japonicus derived from different origins.
The phylogenetic tree showed that each sample was located on an independent branch, suggesting that the concatenation sequence could distinguish among the samples of different origins with more obvious genetic differences. From the phylogenetic tree analysis, samples from Anhui, Guangdong, Guangxi, Hebei, Henan, Hubei, Hunan, Shandong, and Sichuan were well clustered but those from Fujian and Jiangxi showed a close relation. It was hypothesized that as the Fujian and Jiangxi provinces are adjacent to each other and the habitats of L. japonicus in these regions are similar, genetic and evolutionary similarities occurred. Another possibility is that one of these two different provinces may have been introduced with the herb from the other, resulting in close relationship between the plants from different provinces. Overall, the concatenation sequence could provide a good clustering of L. japonicus derived from different regions. Inconsistencies in the evolutionary direction of species were shown to cause differences in the metabolite content (Korte 2021; Zivkovic et al. 2021). Genetic differences in L. japonicus may lead to differences in the primary active constituents, and further chemical analyses are needed to confirm this result.
Chemical Analysis Of The Main Alkaloids
Leonurine and stachydrine, the main active components of L. japonicus, are commonly used as markers to evaluate the quality (Wen et al. 2019). L. japonicus is widely used in the clinic as well as in daily life for treating gynecological diseases (Zhao et al. 2022b); however, the alkaloid content of L. japonicus derived from different regions varies. Therefore, the contents of leonurine and stachydrine were determined using HPLC to investigate the correlation between genetic and chemical content differences. The retention time and peak area of the standards were used as the criteria for leonurine and stachydrine content detection. The HPLC chromatograms (Fig. 4) showed that the total run time for detecting leonurine was 25 min, and the compound peak was detected at a retention time of 4.687 min. The total run time for detecting stachydrine was 40 min, and the peak was detected at a retention time of 19.026 min.
PLS-DA, a well-known technique for feature extraction and discriminant analysis in chemometrics, is used to reveal important patterns related to physiological, genetic, and environmental issues. PLS-DA generates visual scatter plots for the qualitative evaluation of variability among multivariate data, and it is now widely used to assess differences among plant species at the metabolome level (Matsuse et al. 2022; Zhao et al. 2022a). The PLS-DA (R2X = 0.9998) was used to analyze the HPLC data. PLS-DA and PCA score plots were obtained for all samples, wherein each circle represented an independent sample (Fig. 5). The PCA and PLS-DA score plots have better stereoscopic results than the plane ones. The PCA score plot results show that the 27 samples could be divided into 3 groups with small differences. The PLS-DA results showed that the 27 samples could be divided into 7 groups, indicating differences in the content of active ingredients of L. japonicus derived from different origins. The within-group variation was greatest in Henan, and Sichuan and Henan were clearly separated from other areas. Differences between Guangdong and Anhui were small. The current study results showed that the alkaloid content in L. japonicus derived from different regions varied. It has been suggested that environmental factors and genetic differences can affect the synthesis and accumulation of metabolic components, even leading to different drug effects (Zhan et al. 2022).
Association Of Genetic And Main Active Constituent Analyses
A comparison of genetic and chemical analyses revealed that molecular phylogenetic clustering was not fully consistent with PLS-DA. Molecular phylogenetic analysis could distinguish each provenance, but PLS-DA could not distinguish all provenances. The present study results suggest that molecular phylogenetic analysis may be superior to chemical analysis in identifying and classifying L. japonicus derived from different origins. In molecular phylogenetic analysis, Guangshui, Hubei, and Yiyang, Jiangxi, were phylogenetically the most distantly related regions, but their chemical contents were less different, suggesting the role of environment in this finding. Previous studies have shown that environmental factors can activate different signaling pathways that involve the expression of genes related to the biosynthesis or accumulation of secondary metabolites (Jan et al. 2021). Environmental factors have a significant influence on metabolite composition; metabolites are influenced not only by genetic differences but also by environmental factors (Li et al. 2020a). The current study results showed that genetic analysis enables the identification of specific taxonomies, but chemical analysis has some limitations in the identification of species or variants. In such cases, chemical analysis can provide additional information by identifying specific metabolites (Zlatic and Stankovic 2017). Thus, a combination of genetic (molecular evolutionary analysis) and chemical analyses is important to ensure reliable results and avoid incorrect taxonomic identification, thereby improving the identification and quality control of L. japonicus species.